MIG and TIG Welding - Merging Metal

Times change. It wasn't that long ago that if you owned a set of oxy-acetylene gas bottles for welding and cutting you would be considered to have a pretty well-equipped home shop. Maybe you progressed to a stick welder, and most likely moved on from that to a basic MIG welder. I know that's the progression I followed, having possessed a MIG welder at home for the past 20 years now.

However, in recent years the cost of TIG welders has come down significantly, to the point where we expect to see a TIG in any rod shop we visit, and they've made a significant in-road into home shops too. But if you're in the market for a new welder, which is best for you? That depends on a number of variables, probably the most important being what it will be used for. However, let's take a brief look at the differences between MIG and TIG first. We shan't mention gas welding or stick welding here, as they're pretty much"old school" now, though you should know most TIG welders can also operate as stick welders if desired.

MIG (Metal Inert Gas) welding, or wire feed welding, employs a consumable electrode in the form of the filler wire which is fed from the machine through the torch. Depressing the trigger will feed the wire, and as this touches the workpiece it strikes an electric arc, generating heat. Unfortunately MIG welding causes spatter because of this, which can cause damage to nearby objects and can be a fire risk. Another problem with MIG, especially for novices, is that while a perfect looking weld can be produced on top of the workpiece, there is a danger that it hasn't penetrated the metal at all, whereas with the TIG process, the metal is melted before the filler rod is added, ensuring penetration.

While MIG welding is useful when tackling body panels, and doesn't require such exacting tolerances between panels, the weld is harder than in TIG welding, and leaves a higher weld, meaning heat is generated when grinding a MIG weld back (which often isn't required at all with TIG) and the hard weld makes it tougher to work with a hammer and dolly to eliminate any warpage.

Developed originally for the aircraft industry some 60 years ago, TIG (Tungsten Inert Gas) or GTAW (gas tungsten arc welding) as it's also known, uses a non-consumable electrode to strike an electric arc, which produces heat. Similar to oxy-acetylene welding, a filler rod can be used, though it's not always required. The tungsten electrode and the filler rod are protected from the atmosphere by a shield of inert gas, usually Argon, to prevent oxidation of the weld and metal workpiece. The relatively slow speed of TIG means the porosity that can occur with MIG welding is eliminated, while it also produces a smaller heat-affected zone than MIG, reducing the amount of distortion in the metal being worked, as well as reducing stress and the chances of cracking.

TIG welding produces no spatter either, unlike MIG can sometimes do, and the torch is smaller and therefore easier to hold and work with. Unlike MIG, the operator can adjust the heat input whilst welding by using the foot-operated amperage control pedal. However, the work surface has to be extremely clean for TIG welding, especially when welding aluminum, and it is a relatively slow process. If the electrode touches the work it becomes contaminated and must be cleaned immediately, which can be frustrating while you learn to TIG weld, as you'll spend more time removing and cleaning the electrode than actually welding until you get the hang of it! The power source is constant current, either AC, DC, or combination of both (AC/DC), with the type of metal being welded determining which type is used. DC (direct current) is usually used for welding stainless steel and mild and low alloy steels, while AC (alternating current) is used for welding aluminum. TIG welds are smaller, neater and of higher quality than MIG welds, and are what we have come to expect when we see high quality, precision fabrication and chassis work.

4/12Miller's Auto-Set function is perfect for novices. Simply dial in the wire diameter and material thickness and you're ready. It makes set-up easy for novices, though it has a manual mode with infinite voltage control too. It's available on the 140, 180, 211 and 212 machines.

Both MIG and TIG require shielding gases, unless you use a gasless flux core MIG wire, which produces its own shield for the welding process, but we wouldn't recommend buying this type of MIG welder if you plan on doing any serious work with it. MIG welding uses Argon, as well as Argon mixes, such as 1 to 5 percent Oxygen, 3 to 25 percent CO2 or an Argon/Helium mix, while TIG uses Argon, Argon and Hydrogen or an Argon/Helium mix. It all depends on what metal you are welding as to which shielding gas is required. Helium is most often added to increase welding speed or penetration.

While there's a common misconception that anyone can MIG weld (we've all seen bubblegum or pidgeon-poo welds and were probably responsible for some when we were learning to MIG weld!), it's definitely easier than TIG welding, which takes practice and is an acquired skill, albeit very satisfying when you get it right. The superior quality of TIG welds, the precise control offered by the process, and even the appearance of the finished product, seeing as our hobby is as much about appearance as function, means a TIG welder wins over a MIG for chassis fabrication.

The benefits of MIG welding are that it's way easier to weld vertically or even upside down with MIG, less operator skill is required, long welds can be made if distortion isn't a factor, and it's easier to learn. Benefits of TIG welding are superior quality welds, precise control of heat input, it's spatter-free and offers low distortion and minimal cleanup. It also looks great!

Whether you're learning to MIG or TIG, you're going to have to master the machinery, though most MIG welders these days carry a chart inside the casing where the wire spool mounts, guiding you to the correct wire speed and heat settings for the thickness of metal you're planning to weld. TIG welding is more complicated and until recently the bewildering array of knobs and switches on a TIG welder meant you had to really know what you were doing to set the machine up. Miller has made things easier with the introduction of not only its 212 Auto-Set MIG, on which you simply set the wire size and metal thickness before welding, but also with the revolutionary Diversion 165 AC/DC TIG, on which you just set the material type and thickness. We've used the latter at Miller's Southern California facility during one of their training days, and actually preferred it to the considerably more complex and expensive Dynasty 200, finding it easier to use (for a novice-I may have been MIG welding for 25 years but can count the times I've TIG welded on both hands) though the latter is designed more for industrial use admittedly. The Diversion 165 also offers fingertip control of the heat input, thanks to the amperage control on the Weldcraft LS17 torch, though a more regular (for TIG) foot pedal can also be used.

I attended the training session with the intention of learning to TIG weld aluminum, as I was about to start fabricating an all-aluminum roof for my roadster pickup, and the Diversion 165 proved ideal However, Miller also has a spool gun which allows their newer MIG welders to easily convert to weld aluminum too, which I had previously used and found to be a great tool. This is compatible with, and easily attaches to, the 212 Auto-Set and Millermatic 252 as well as Miller's Passport Plus, and by simply switching to Argon shielding gas you're ready to tackle welding aluminum. In fact on the 252 the machine automatically detects which gun you're using when you pull the trigger. Speaking of Miller's Passport Plus, it's a compact MIG welder that not only contains a gas bottle and 8-inch spool of wire inside a 45lb package, but it can be plugged into either 115 or 230 V power using Miller's Multi-Voltage Plug for a truly portable welder. Probably not what you need in your shop but ideal for working up ladders or down holes!

Of course Miller isn't the only company making welders, and companies such as Lincoln Electric and HTP America offer MIG and TIG welders. I'd suggest doing a little research and making a decision on what's right for you and what you'll be working on, or may want to work on in the future. All the welder suppliers have websites that are informative and can guide you through any questions, with Miller's being particularly helpful. In fact, if you visit the "Order Literature" tab at www.millerwelds.com, you can download a TIG Buyer's Guide.

One thing we haven't touched on so far is what size welder you might require. The small portable MIG welders are very handy and easy to move around, but are they up to the task of chassis fabrication for instance? They are classified by how much amperage they can generate at a given duty cycle, which is determined as the number of minutes the welder can operate in a ten minute cycle before it needs to cool. Thicker metals require more amperage than thinner gauges too, so while a 130 or 150 amp MIG welder with a 30 percent duty cycle may suffice for small shop jobs up to 3/16-inch thick, you may be better opting for a 200 or 250 amp MIG with a 40 to 60 percent duty cycle if you plan on tackling heavier fabrication. If you're going to spend the money, why not just spend it once?

So which to choose? MIG is easier to learn, is capable of welding light gauge or thick material, and will weld all common metals, from mild steel to stainless and even aluminum if you change gas and use Miller's spool gun (assuming you have a new Miller welder!), and is faster. TIG offers precise welding on thin material with less distortion than MIG, produced high quality, smaller, and good looking welds, can weld steel and aluminum with Argon, without swapping bottles, and offers adjustable amperage control while welding. You pays yer money and takes yer choice, though if it were my preference, I'd opt for the TIG, even though a MIG is perfectly capable of chassis work, but then I already have a MIG, so I would say that wouldn't I?!